Hiding "lastest rendered frame" in renderfarm sheepit for confidentiality?
The core concept of Sheep It involves transferring the project being rendered on other people's machines. As the Sheep It owners have no control over the 3rd party computers, keeping work private is a challenge.

There are, however, paid solutions (for instance, RenderStreet) that can get the job done without breaking the bank and in complete security. As working professionally implies receiving monetary compensation for the projects, the rendering costs can be factored in the project budget.

As a final comment, I would recommend checking the privacy policy of any service you intend to use for professional work.